1. Field of the Invention
The present invention relates to a varnish coating device and a method for coating a varnish, in more particular, to a varnish coating device for coating a varnish to a wire and a method for coating a varnish.
2. Related Art
In fabrication of a wire such as an enamel wire, a wire fabricating device in that a roller is dipped into a coating bath fulfilled with a varnish, and the varnish is applied to a wire by continuously contacting the wire to a top face of this roller, thereafter the varnish applied to the wire is baked in a baking furnace has been used. Japanese Patent No. 3455564 discloses an example of such an enamel wire fabricating device.
In addition, a varnish coating device in that a varnish introducing plate having plural slits, a protecting plate, a sealing plate, and an inclined plate are layered on one side of a varnish tank having an opening at its upper part, and a varnish is filled at a predetermined position of the slit. A wire is passed through the slit to be inserted into a semi-divided hole formed in a part of the slit, thereby coating the varnish on the wire. Japanese Patent Application Laid-Open No. 2004-230324 discloses an example of such a varnish coating device.
This type of varnish coating device is provided with a varnish circulating path which supplies the varnish of a constant quantity to the coating bath, the varnish tank or the like and collects the varnish therefrom, so that the varnish of the constant quantity is pooled in the coating bath and the varnish tank, in order to conduct the coating stably.
As a conventional varnish for an enamel wire, a one-pack type (poly)urethane varnish has been used. The one-pack type (poly)urethane varnish comprises a first varnish material A and a second varnish material B each comprising a principle component having a functional group different from each other. The functional group of the first varnish material A is masked with a masking which is removed by heating, and the functional group of the second varnish material B is not masked with this masking, and the first varnish material A and the second varnish material B are mixed together with a solvent, a block agent or the like to provide a one liquid (one-pack).
This one-pack type (poly)urethane varnish does not react at a normal temperature, even though the first varnish material A is mixed with the second varnish material B, since the functional group of the varnish material A is completely masked with the masking. In the baking process, the masking is removed at a temperature of around 100° C., and the solvent is evaporated in a heating atmosphere of not less than 200° C., so that the first varnish material A and the second varnish material B are urethane-bonded. Therefore, it is possible to use the one-pack type (poly)urethane varnish in the conventional varnish coating device in which the varnish is circulated prior to the baking process.
In the one-pack type (poly)urethane varnish, an organic solvent such as phenol, cresol, and xylene is used. However, environment pollution, poisoning of living body and the like caused by the organic solvent are concerned. In addition, a price of the solvent rises suddenly due to a sudden rise of naphtha and decrease of energy resources, or the like in late years, an economical efficiency of the organic solvent is deteriorated. Therefore, a two-pack type (poly)urethane varnish using a low boiling point solvent such as acetate based solvent instead of using the organic solvent such as the cresol, phenol, and the block agent is remarked. For example, Japanese Patent Laid-Open No. 2006-045484 discloses such a two-pack type (poly)urethane varnish. In addition, since a reaction rate and a curability of the two-pack type varnish are high, it is necessary to finish the work in a short time, when applying the two-pack type varnish as an insulating coating.
Compared with the one-pack type varnish, the two-pack type varnish has following advantages.
(1) It is possible to reduce a solvent component in the varnish to be lower than half, thereby saving the resources.
(2) It is possible to reduce CO2 discharged from the baking furnace to be lower than half, thereby reducing a burden on the environment.
(3) It is possible to lower a baking temperature, thereby reducing power consumption.
However, according to the conventional varnish coating device, all the varnish supplied in the coating bath or the varnish tank is not applied to the wire passing therethrough (traveling wire), and the varnish which is remained without being applied is circulated to the coating bath through the varnish circulating path. Therefore, it is impossible to apply the conventional varnish coating device to the two-pack type varnish that transforms (cures) in a short time during the circulation.
Accordingly, it is an object of the present invention to provide a varnish coating device for coating a varnish to a wire and a method for coating a varnish, by which the varnish can be applied to the wire without causing any problem, even if the varnish that transforms (cures) in a short time is used.
According to a first feature of the invention, a varnish coating device comprises:
a coating die for applying a varnish to a wire;
a varnish bath for supplying the varnish to the coating die by a self weight of the varnish; and
a varnish feeding part for supplying the varnish to the varnish bath.
In the varnish coating device, the varnish bath may be configured to flow the varnish toward the coating die without stagnation.
In the varnish coating device, the varnish bath may be connected to the coating die to have an L-shape.
In the varnish coating device, the coating die may be provided with a hole for inserting the wire, and a direction of the hole is aligned with a direction of passing the wire.
In the varnish coating device, the varnish bath may be connected to the coating die directly or via a tube.
In the varnish coating device, the tube may be connected to the coating die with a curvature or a right angle.
In the varnish coating device, the tube may comprise a material has an elasticity and an insolvability with a solvent contained in the varnish.
The varnish coating device may further comprise:
a sensor for detecting a quantity of the varnish supplied to the varnish bath; and
a control unit for controlling the quantity of the varnish supplied to the varnish bath based on a detection result of the sensor.
According to a second feature of the invention, a method for coating a varnish comprises:
a first step of supplying a varnish from a varnish feeding part to a varnish bath;
a second step of supplying the varnish in the varnish bath to a coating die by a self weight of the varnish;
a third step of passing the varnish and a wire through the coating die to form a varnish layer of the varnish with a predetermined thickness on a surface of the wire; and
a fourth step of baking the varnish layer to form a coating film.
In the method for coating a varnish, the second step may comprise flowing the varnish toward the coating die without stagnation.
In the method for coating a varnish, the first step may comprise supplying the varnish to keep the quantity of the varnish in the varnish bath to be constant.
In the method for coating a varnish, the third step and the fourth step may be repeated until the coating film on the surface of the wire has a desired thickness.
In the method for coating a varnish, the varnish may comprise one-pack type varnish.
In the method for coating a varnish, the varnish may comprise plural-pack type varnish.
According to the present invention, it is possible to apply the varnish to the wire without causing any problem, even if the varnish which is transformed (cured) in a short time is used.